ci: add windows-latest to test matrix #125

Job	Run time
pytest (windows-latest)	53s
API integration tests + coverage (ubuntu-latest)	16s
Verify prod requirements.txt is sufficient	10s
API integration tests + coverage (windows-latest)	35s
Frontend unit tests (vitest) (windows-latest)	38s
Frontend unit tests (vitest) (ubuntu-latest)	14s
mypy	19s
pytest (ubuntu-latest)	18s
	3m 23s

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